The present invention relates to internal combustion engine valve seals and retainers, and more particularly to a unitary annular retainer including an integral spring seat where the retainer provides support to an entire outer circumference of a valve stem seal.
In conventional overhead valve, internal combustion engines, at least two valves reciprocate to provide intermittent communication between intake and exhaust manifolds and a combustion chamber. The valves include valve stems that are commonly disposed in valve stem guides, supporting axial motion in an engine component such as an engine head. Lubrication is provided to upper portions of the valve stems by a spray of lubricating oil within a valve cover disposed over the engine head or by gravity flow from an associated rocker arm. Oil flows along a free upper end of the valve stem toward the manifolds and valve heads by the force of gravity and may be encouraged by a pressure differential in the manifold versus crankcase pressure.
Annular valve stem seals are generally urged into contact with the outer surface of the valve stem and an upper portion of the valve guide by a valve stem seal retainer, and serve various purposes. First, valve stem seals minimize engine oil consumption by restricting oil entry into the manifold and the combustion chamber. Second, they help to minimize exhaust particulates that contribute to pollution. Third, they are helpful in minimizing guide wear, which is of particular importance in large diesel engines due to the nature of their operation. The valve stem, valve guide, and valve stem seals are annularly wrapped by a helical compression valve spring that serves to bias the valve into a closed position. The longitudinal ends of the valve spring are restrained by flanges on corresponding valve spring retainers and/or spring seats, thereby maintaining proper alignment and position of the valve and valve spring.
In the heavy-duty engine market, a number of changes are being made to comply with recent and prospective emissions standards. As the construction of the engine changes, engine designers must nevertheless maintain a robust engine design with a sufficient level of dependability. One of the more prominent changes being implemented is the increase of the power rating of the engine in an effort to reduce the size of the engine. In particular, engine manufacturers are attempting to reduce the displacement of heavy-duty engines while still providing ample horsepower and torque for heavy-duty applications. As is well-known, engine displacement is calculated by multiplying cylinder bore area times the piston stroke length. In reducing the displacement of heavy-duty engines, manufacturers are reducing both the bore area and the stroke length while increasing the compression within the combustion chamber. Increasing the required amount of compression, in turn, places greater stress on the valve seal. Many of these engines are increasing their compression by up to 50-60 psig, which is a far greater pressure than many prior art valve seals can handle while being properly retained on a valve guide. For such cases, an integral valve seal with a metal retainer is normally recommended.
However, as the bore area of an engine is reduced, the area provided for valve assemblies above a combustion chamber is correspondingly reduced. The problem is especially significant in heavy-duty diesel engines because all valve assemblies are typically oriented perpendicular to the engine head. Additionally, a fuel injector occupies a large portion of the area above the cylinder bore. Thus, in high efficiency heavy-duty diesel engines having more than two valves (intake and exhaust valves) per cylinder, the area directly above the engine bore must be shared by a fuel injector and the valves. Since the size of the fuel injector is substantially fixed, a reduction in engine bore generally requires a reduction in the valve assembly diameter, including corresponding reductions in the diameter of valve stem seals, valve guides, and valve stem seal retainers. There is thus a need for a valve seal assembly capable of withstanding increased compression loads while providing a seal having close clearance and durability.
Another way manufacturers are attempting to comply with recent and prospective emissions standards is by turbocharging heavy-duty diesel engines while also incorporating exhaust gas recirculation (EGR) to reduce emissions. In typical turbocharged, unthrottled (i.e. diesel) engines that do not have EGR, the intake manifold pressure is slightly higher than the exhaust manifold pressure. Thus, if the valve stem seal is strong enough to withstand the intake manifold pressure, it will also withstand the lower exhaust manifold pressure. However, once EGR is incorporated, a portion of the exhaust gases are injected back into the intake manifold at a point downstream of the turbocharger compressor. To effectively inject exhaust gases into the intake manifold, the exhaust manifold pressure must exceed the intake manifold pressure. In one design, the exhaust manifold pressure must be 75-100 percent higher than the intake manifold pressure to achieve the desired level of exhaust gas recirculation. However, it has been found that prior art integral valve seal designs are insufficiently supported by the metal retainer to operate in high pressure environments. In particular, such a dramatic increase in exhaust manifold pressure has caused xe2x80x9cburstingxe2x80x9d of the valve seal in experimental turbocharged unthrottled engine designs using EGR, resulting in loss of compression and seal integrity. Thus, a reinforced integral valve seal assembly is desired that is capable of withstanding increased compression loads while also providing a seal having close clearance and durability to minimize the possibility of valve seal failure in high pressure environments.
The present invention is directed to an integral valve stem seal and valve stem seal retainer designed to withstand high manifold pressures. The retainer includes concentric lower and upper portions, where the portions are separated by diameter-reducing transition zone. As a result, the upper portion has an inside diameter less than the lower portion. An elastomeric annular sealing member engages the upper portion of the metal retainer such that the entire outside circumference of the sealing member is reinforced by the retainer. An annular flange extends radially outwardly of the lower portion of the retainer to engage at least one coil of a valve spring. The annular sealing member includes a plurality of oil or gas seals that engage an outer surface of a valve stem, and further includes a lower lip that engages an upper surface of a transition of a valve guide. The lower portion of the retainer may also include a plurality of radially inwardly extending tangs to positively engage an outer surface of the valve guide against axial and rotational movement.
Because the valve stem seal is reinforced along its entire outside circumference, the inventive seal is extremely strong and resistant to failure even though the outer diameter has been reduced to accommodate smaller, higher power-density engines. Moreover, since the reinforcement on the seal is provided by the upper retainer portion, which has the smallest inner diameter, the seal is extremely resistant to blow-out or xe2x80x9cburstingxe2x80x9d. Thus, the seal of the present invention may be used in new, higher pressure heavy-duty engines to reduce the likelihood of valve stem seal failure.